Downing Street is backing the minister's version of events - that Mr Sixsmith told Sir Richard Mottram he was resigning and that this information was passed on to the transport secretary.

Mr Blair's official spokesman said it was "pretty obvious" the transport department press office had been "dysfunctional to say the least".

He praised Mr Byers for making the difficult decisions necessary to start improving public transport.

Mr Sixsmith has said he has an 18,000-word dossier which exonerates him and makes it clear he did not resign.

'Spreading stain'

He also says he was offered another job within the civil service and "compensation" if he signed a retrospective letter of resignation.

Mr Sixsmith says he still has a civil service job because he has not resigned. On Monday, outside his home, he appeared briefly to say he could not comment further.

Mr Byers is coming under continued pressure, with Labour backbencher Gordon Prentice saying people needed to know what Mr Byers knew when he made the resignation announcement.

Mr Sixsmith reportedly had a row with Jo Moore

"This whole business is like a spreading stain and the question is who next is going to be contaminated by it," said Mr Prentice, a member of the Commons public administration select committee.

But the MP said the row should not be personalised but focus on how to protect the civil service.

The transport secretary said nothing as he left his Newcastle constituency home on Monday, with reporters asking if he would resign.

But speaking on ITV's Dimbleby programme on Sunday, My Byers said that "someone perhaps has forgotten exactly what did happen" on the resignations.

The row began with a reported disagreement between Mr Sixsmith and Ms Moore over whether rail statistics should be published on the day of the royal funeral.

'Bad pattern'

The Conservatives say the row shows Mr Byers is incapable of running his department and should resign.

Shadow Cabinet Office minister Tim Collins told BBC Radio 4's Today programme the argument followed a pattern of Mr Byers giving different versions of events to the Rover and Railtrack chairmen.

"At best most people will conclude that Mr Byers is a shambolic incompetent, at worst they will think he's a pathological liar," said Mr Collins.

Liberal Democrat leader Charles Kennedy said Mr Byers owed it to the public, the government and to transport policy to step aside.

The tide of claims and counter-claims on this and previous controversies meant the minister could no longer do his job, Mr Kennedy told BBC News.

Special adviser scrutiny

Sir Alistair Morton, who clashed with Mr Byers before resigning early as head of the Strategic Rail Authority, criticised Downing Street's "relentless daily interference" in the transport department.

The relationship between special advisers and civil servants comes under scrutiny from the Commons public administration committee this week.

Jonathan Baume, general secretary of the First Division Association, which represents senior civil servants, including Mr Sixsmith, will appear before that inquiry.

Mr Baume told Today the latest row meant the government should act on its promise to produce a Civil Service Act to enshrine in law the political impartiality of civil servants.

Andy Wood, who was pushed out as a press chief soon after Labour came to power, said the warnings about the civil service expressed by himself and two other ex-communications directors in 1998 were now coming true.